1. Field of the Invention
The present invention generally relates to electro-optical readers for reading indicia, for example, bar code symbols, having parts with different light reflectivities and, in particular, to a control switch arrangement for, and a method of, controlling different operational states in such readers.
2. Description of the Related Art
Various electro-optical readers have previously been developed for reading bar code symbols appearing on a label, or on a surface of a target. The bar code symbol itself is a coded pattern of indicia. Generally, the readers electro-optically transform graphic indicia of the symbols into electrical signals which are decoded into alphanumeric characters. The resulting characters describe the target and/or some characteristic of the target with which the symbol is associated. Such characters typically comprise input data to a data processing system for applications in point-of-sale processing, inventory control, article tracking and the like. Electro-optical readers of this general type have been disclosed, for example, in U.S. Pat. Nos. 4,251,798; 4,369,361; 4,387,297; 4,409,470, 4,760,248 and 4,896,026, all of which have been assigned to the assignee of the present invention.
As disclosed in some of the above patents, a particularly advantageous embodiment of such a reader resided in emitting a laser light beam from a hand-held, portable laser scanning head which was supported by a user; aiming the head and, more particularly, the laser light beam, at a symbol to be read; repetitively scanning the laser beam in a series of scans across the symbol; detecting the scanned laser light which is reflected off the symbol; and decoding the detected reflected light. Inasmuch as the laser light beam was usually, but not always, generated by a helium-neon gas laser which emitted red laser light at a wavelength of about 6328 Angstrom units, the red laser light was visible to the user and, thus, the user, without difficulty, could properly aim the head and position and maintain the emitted red laser light on and across the symbol during the scanning.
However, in the event that the laser light beam was generated by a semiconductor laser diode, as, by way of example, see U.S. Pat. Nos. 4,387,297; 4,409,470 and 4,460,120, then the aiming of the head relative to the symbol was rendered more difficult when the laser diode emitted laser light which was not readily visible to the user. For some laser diodes, the laser light was emitted at a wavelength of about 7800 Angstrom units, which was very close to infrared light and was on the borderline of being visible. Even with the advent of laser diodes whose emitted light was in the visible wavelength range, ambient light tended to mask out the laser diode light. Furthermore, if the laser diode light was moving, for example, by being swept across the symbol, and especially if the laser diode light was being swept at fast rates of speed on the order of a plurality of times per second, for example, at a rate of 40 scans per second, then the laser diode light was not readily visible to the user, even in a darkened room. Hence, due to one or more of such factors as the wavelength of the laser light, the intensity of the laser light, the intensity of the ambient light in the environment in which the laser light was operating, the scanning rate, as well as other factors, the laser diode light was rendered “non-readily visible”.
This non-readily visible laser diode light did not enable the user, however, to readily aim the laser diode light at the symbol, at least not without some difficulty and practiced effort because, simply put, the user could not see the laser diode light. The user, therefore, was required to hunt around by trial and error, hope that the scanning laser diode light was eventually properly positioned on and across the symbol, and wait until the scanning system advised him, typically by the lighting of an indicator lamp or by the sounding of an auditory beeper, that the symbol had indeed been successfully decoded and read. This hunting technique was a less-than-efficient and time-consuming procedure for reading symbols, particularly in those applications where a multitude of symbols had to be read every hour and every day.
In an attempt to enable the user to readily aim the laser diode light at the symbol, U.S. Pat. No. 4,835,374 proposed an aiming light arrangement to assist the user in visually locating and aiming the head at each symbol when non-readily-visible laser light was employed. The aiming light arrangement utilized a visible light source, e.g., one or more light emitting diodes, which was separate and distinct from the laser light source. A manually-operated trigger was employed to actuate the aiming light arrangement in a first operational state of the trigger for visibly illuminating a region on the symbol. This visible region was used for aiming purposes. Thereupon, in a second operational state of the trigger, the laser light source was actuated, thereby initiating the reading of the symbol.
Symbols can also be read by employing imaging devices. For example, an image sensor device may be employed which has a two-dimensional array of cells or photosensors which correspond to image elements or pixels in a field of view of the device. Such an image sensor device may include a two-dimensional or area charge coupled device (CCD) or complementary metal oxide semiconductor (CMOS) device and associated circuits for producing electronic signals corresponding to a two-dimensional array of pixel information for a field of view.
It is therefore known to use a CCD for capturing a monochrome image of a barcode symbol to be read as, for example, disclosed in U.S. Pat. No. 5,703,349. It is also known to use a CCD with multiple buried channels for capturing a full color image of a target as, for example, disclosed in U.S. Pat. No. 4,613,895.
For many applications, the imaging device is accommodated in a hand-held package which may be pistol-shaped. Moreover, such imaging devices are typically equipped with external lighting to illuminate the symbol to be captured. In addition, such external lighting serves as an aiming source to indicate to the operator just where the symbol is located relative to the cellular array.
In another known attempt, U.S. Pat. No. 5,117,098 disclosed a multi-state trigger using dual, double-action switches. However, the known double-action switches are not altogether satisfactory from an ergonomic point of view and typically require a long travel stroke between actuations of the switches, as well as some sort of positive tactile feedback for at least one of the switches, and also require a relatively high actuation force to control the switches. All of these factors, plus the lack of availability of high precision switches capable of very long working lifetimes, have proven disadvantageous in making such readers as ergonomically efficient as possible.